A railroad switch is a well-known mechanical installation that enables railway trains to be guided from one set of tracks to another set of tracks.
FIGS. 1A-1B show a typical railroad switch located at the intersection of main tracks 101 and secondary tracks 102. The railroad switch has switch points 104 which are mechanically linked so that they move together when toggled from one position to another. As a train approaches the railroad switch along the main tracks 101 and in the facing-point direction, the train wheels are guided along the route determined by which of the two switch points 104 is connected to the track facing the switch. If the left point is connected, as shown in FIG. 1A, then the left wheels of the train will be guided along the rail of that point, and the train will diverge to the right onto the secondary tracks 102. If the right point is connected, as shown in FIG. 1B, then the right wheels will be guided along the rail of that point, and the train will continue along the main tracks 101. The mechanical link between the switch points 104 ensures that only one of them may be connected to the facing track at any given time.
In FIG. 1A, if the train travels on the secondary tracks 102 but in the trailing-point direction, when the left point of the switch is connected, the train will continue onto the main tracks 101 without any issue. However, if the train travels on the main tracks 101 in the trailing-point direction, while the left point of the switch is connected, the train wheels will force the switch points 104 to switch to the right to allow the train to continue through on the main tracks. Such trailing of an open switch is referred to as a “run-through.” A similar run-through could occur from the secondary tracks 102 when the switch is configured to allow train movements along the main tracks 101, as shown in FIG. 1B.
After a railroad switch has been run through, it could be in one of a number of conditions. Assuming the switch is in the condition as shown in FIG. 1A before the run-through, FIGS. 2A-2B show potential conditions of the switch after the run-through. For example, the switch may return to its previous position as set before the run-through, which is shown in FIG. 2A. For another example, the switch may be damaged by the run-through and rest in an “in-between” position that connects neither the main tracks nor the secondary tracks, as is shown in FIG. 2B. Even if the switch remains connected in the run-through position (in this case, switched to the right side like in FIG. 1B), the points are usually not tightly closed or locked in that position.
These post-run-through switch conditions may be problematic if a train somehow moves in reverse through the switch. For example, if the switch is damaged and remains in an “in-between” position as shown in FIG. 2B (or otherwise not securely closed or locked in the run-through position), the train wheels moving in reverse (i.e., in facing-point direction) will not be properly guided by the switch, which could cause derailment of the train. Even if the switch has returned to its pre-run-through position as shown in FIG. 2A, the reversing train could travel too fast for the switched curve to the secondary tracks, again potentially causing derailment.
In view of the foregoing, it may be understood that there are significant problems and shortcomings associated with current railroad switches.